Application of an Impedimetric Technique for the Detection of Lytic Infection of Salmonella spp. by Specific Phages

Abstract

This study was performed to evaluate the adaption of the impedimetric method to detect the lytic infection by Salmonella-specific bacteriophages and to provide a higher selectivity to this rapid method in detecting Salmonella spp. by using specific agents. Three bacteriophages and twelve strains of Salmonella spp. were tested. Each of the twelve strains was used separately to inoculate TSB together with each one of the phages. The inoculum concentration was between 10(6) and 10(7) cfu/mL, at a cell: phage ratio of 1 : 100. From the sample analysis, based on conductance (G) measurements (37 degrees C), the infection could be detected, by observation of both detection-time delay and distinct curve trends. The main conclusions were that kinetic detection by impedance microbiology with phage typing constitutes a method of determining whether a test microorganism is sensitive to the bacteriophage and a method to evaluate whether a lytic bacteriophage is present in a sample, by affecting bacterial growth rate/metabolic change.

Figure 1

Detectable change in electrical characteristics checked at several bacteria densities. There were considered the mean values of duplicates from three experiments made for a representative phage (2/2) and its bacterial host (S1400/94): (a) 10⁴ cfu/mL; (b) 10⁵ cfu/mL; (c) 10⁶ cfu/mL; (d) 10⁷ cfu/mL; (e) 10⁸ cfu/mL; (f) 10⁹ cfu/mL.

Figure 2

Effect of cell : phage ratio on the detection times and percentage change of conductance of 2/2 bacteriophage host S1400/94. These values were obtained from three experiments, in duplicate. Cell : phage ratio—(a) 1 : 0; (b) 1 : 0.1; (c) 1 : 1; (d) 1 : 10; (e) 1 : 100.